Project Summary Immunosuppressive macrophages have been linked to cancer-related inflammation and therapeutic resistance in cancer including chemotherapy and immunotherapy, thus representing attractive therapeutic targets. Macrophages can be polarized into extreme M1 or M2 phenotype depending on the environmental cues. Although macrophage phenotype within the tumor microenvironment is more complicated, it is clear that immunosuppressive tumor-associated macrophages (TAM) phenotypically more resemble M2-like macrophages. In the preliminary studies, we discovered that transcription factor c-Maf is highly expressed in mouse and human polarized M2 macrophages and immunosuppressive TAM. In addition, natural product yeast-derived particulate ?-glucan treatment significantly downregulates c-Maf expression leading to enhanced T cell responses in mice. We also demonstrated that M1 and M2 macrophages have distinct metabolic profiles and c-Maf regulates many genes related to glycolysis. Based on these preliminary studies, we hypothesize that transcription factor c-Maf is an essential controller and a metabolic checkpoint for immunosuppressive TAM functional activity. Three Aims are proposed. Aim 1 determines the cellular and molecular mechanisms by which c-Maf is regulated in immunosuppressive TAM. We will investigate whether tumor secreted factors regulate c-Maf expression in TAM. We will also determine how the Raf-1 kinase pathway regulates c-Maf and c-Maf-related gene expression. Finally, we will test whether loss of function of c-Maf in TAM significantly delays tumor progression and metastasis. Aim 2 determines which TAM metabolic pathway(s) is regulated by c-Maf using systems metabolomics approach. We will first determine TAM metabolic pathways using Stable Isotope Resolved Metabolomics (SIRM) approach. Furthermore, we will determine which metabolic pathways are regulated by c-Maf. Finally we will determine the causative role of metabolic reprogramming in ?-glucan-mediated TAM functional conversion. Aim 3 determines whether the dectin-1 agonist ?-glucan modulates TAM function of human non-small cell lung cancer (NSCLC) via the c-Maf pathway. We will determine whether ?-glucan treatment downregulates c- Maf expression and alters c-Maf-regulated genes in human NSCLC TAM. We will also determine whether human TAM functions are reversed upon ?-glucan treatment. Finally, we will examine whether ?-glucan treatment in patients with NSCLC downregulates c-Maf expression and alters monocyte suppressive function. The overall goal of this proposal is to understand the transcriptional regulation of immunosuppressive TAM by c-Maf and establish the transcription factor c-Maf as a novel target for human cancer immunotherapy.